This invention relates to logic circuits for D.C. proximity or limit switches and in particular to circuits which are protected from and indicate shorted or open load conditions and which can be switched from normally open (N.O.) to normally closed (N.C.) and vice versa.
It is known in the prior art to provide flashing indicators by means of an oscillator powering a light-emitting diode (LED). It is also known generally that a silicon-controlled rectifier (SCR) or programmable unijunction transistor (PUT) can be used to protect a power switching element, such as a transistor, from overcurrent. It would be desirable and advantageous, however, to provide a proximity or limit switch which indicates a shorted or open load via a flashing indicator, protects its power switching elements from such shorted or open loads, and which can be readily changed from a normally open switch to a normally closed one and back.